Electric heater and method of making the same



Sept- 28, 1954 A, P. CHARBONNEAU 2,690,490

ELECTRIC HEATER AND METHOD oE MAKING THE SAME IS f 2 Sheets-Sheet 2 A.P. CHARBONNEAU Sept. 28, 1.954

ELECTRIC HEATER AND METHOD OF MAKING THE SAMEv Filed July 23, 1.951

Patented Sept. 28, 1954 ELECTRIC HEATER AND METHOD OF MAKING THE SAMEAllan P. Charbonneau, Wauwatosa, Wis., assignor to Cutler-Hammer, Inc.,Milwaukee, Wis., a corporation of Delaware Application July 23, 1951,serail No. 238,160

6 Claims.

This invention relates to improvements in electric heaters and methodsof making the same; and the invention relates more particularly tosheathed electric heaters of the strip type.

A primary object of the invention is t generally improve the structuraland operative characteristics of electric heaters of the aforementionedtype.

Another object is to facilitate production and assembly of the heaterparts.

Another and more specic object is to provide an impro-ved electricheater employing a resistor in the form of an elongated helixl whereby along and efficient resistor path is insured.

Another object is to provide novel means for properly anchoring theresistor during and after lling of the sheath with a granularnoncementitious insulating material.

Another object of the invention is to provide an improved method ofmaking electric heaters of the aforementioned type.

Other objects and advantages of the invention will hereinafter appear.

In the drawings accompanying this application, I have shown for purposesof illustration several forms which my invention may assume, and inthese drawings Figure 1 is a fragmentary bottom plan View with the baseportion of the sheath removed and showing an arrangement with terminalsat either end;

Fig. 2 is a fragmentary side elevational view of a partially assembledheater positioned vertically to facilitate the filling operation;

Fig. 3 is a fragmentary side elevational View of acompleted embodimentof the invention having terminals at each end;

Fig. 4 is a fragmentary top plan view of the strip heater illustrated inFig. 3;

Fig. 5 is a fragmentary side elevational View of the embodiment havingboth terminals at one end of the heater and having part of the sheathbroken away, and

Fig. 6 is a fragmentary top plan view of the strip heater illustrated inFig. 5.

Referring to Figs. l through 4, the numeral Ie designates one of thepunched and stamped sheet metal parts of a sheath or casing, said partbeing formed to provide a recess lub of substantially rectangular formboth in transverse and longitudinal cross section and the same havingrelatively narrow longitudinal flanges II)c and relatively large enolriianges Ild. Recess IIIb is provided in its bottom wall adjacent to eachend thereof with relatively large openings we which are preferably ofcircular contour. Located within said ends of recess Ib are. plates Ilof insulating mat-erialsuch` as mica. Plates l! are provided withopenings I Ia just sufciently large to accommodate the threaded shank I2of a bolt having a hat head i221. interposed between said plate I I andbolt head I2n are an insulating member i3 and a sheet metal part I 4i.Said sheet metal part I l is provided with an aperture I la to slidablyaccommodate the shank I2 of the above mentioned bolt and is fastened tothe shank side of the flat head I 2.a as by means of welding. Said sheetmetal part I is also constructed with a lip or upturned end portion Mbas shown in Fig. 2. The insulating member I3 is also constructed With anaperture i3 to slidably receive the shank i2 of said bolt. Saidinsulating member I3 is assembled in juxtaposition with plater I I andis constructed with an aperture I3,b to receive the above-mentioned lipMb of the sheet metal member i4. The plate ii and insulating member i3are of such dimensions as to iit against the bottom wall of recess Iband to bear slightly against the side walls of said recess to prohibitany rotational displacementr between either of said members and thecasing part lila. It is apparent that the engagement between the lip hiband the aperture isb of said insulating member I3 prevents rotationalmovement of said sheet metal part Iii and said bolt with respect tothecasing part Ilia.

Rigidly attached to the ilat head I'a of the bolt as by spot-welding isa punched andl stamped sheet metal bracket l5,y said bracket being ofsubstantially U-shape and having end portions ia and lla thereof odsetfrom the flat head lia of the bolt. The ends I5a and Ib of bracket I5are relexed or hook-shaped, as best illustrated in Figs. 1 and 2.

Attached to the bracket I5 by means of the hook-shaped end portion 55his an insulating ring I t. Said insulating ring ES is. constructed ofmica or any well known insulating material and although it may beconstructed to any desired shape the preferred construction is as shownin Fig. l. Also attached to said insulating ring it is a sheet metalsupporting member il so positioned on said ring IE as to preventelectrical conductivity between the bracket I5 and said member II. Saidsupportingmember I'I is constructed with a reflexed portion and engagesthe ring I6 in the same fashion as bracketl l5 engages said ring I6.Supporting member I1 is also constru-cted with a curved arm Ila toreceive a helical resistor 23 whenv said resistor 23 is subsequentlyreflexed between the terminals.

lA mica insulating washer is strung upon the 3 shank I2 of the bolt andfits within the opening Ic in the bottom wall of recess Ib at one end ofthe latter. A relatively larger mica washer I9 is then strung upon shankI2, then a metal washer and a nut 2I which is adapted to clamp all theparts of the terminal to the sheath part I Qa. A second nut Z2threadably engages said shank I 2 of the bolt so as to provide a meansfor clamping a circuit wire (not shown) between the nuts 2l and 22. Theterminals at each end of the casing part Iiiet are of identical form andare attached in a like manner.

The heating element 23 is constructed of a wire preferably composed of aknown alloy of nickel and chromium which is adaptable for use as aheater resistor and is formed into an elongated helix of relativelysmall diameter. A coil of relatively small diameter is used to overcomethe excessive sagging inherent in large diameter helical resistors.

The resistor 23 is initially assembled within the recess IIIb by rigidlyattaching one of the free ends of said resistor to one of the hookedends I5a of a bracket I5. This is accomplished by inserting the free endbetween the arms of said hooked end and then pressing said arms togetheras by means of a pliers to provide a good mechanical and electricalconnection between the same and the end of the wire. Resistor 23 thusanchored is then extended toward the second terminal and reflexed aboutthe supporting member I'I of said second terminal. This step is thenrepeated so as to bring said resistor 23 back toward the first terminaland reflex it about the supporting member Il attached to said firstterminal member. After the second reflex operation the resistor isextended toward and fastened to the arm I5a of the second terminal inthe same fashion as the resistor 23 was initially anchored to the rstterminal as above described. It is an essential feature of thisinvention that the resistor 23 be kept reasonably taut so as to preventexcessive sagging thereof throughout subsequent operations.

With the terminal members and the resistor 23 thus positioned within andattached to the sheath part Illa, a cover plate 24 is attached to thelatter. Said cover plate 24 has one of its ends 24a bent over one of theend anges IIlb of sheath part Ii)a and its longitudinal edges 24b bentover a major portion of the length of flanges I0C to provide a seamconnection between the sheath parts. As shown in Fig. 2, however, e.portion of the seam connection is left incompleted and the unattachedend of cover 24 is bent or curved outwardly to provide an opening atthat end of the sheath. The sheath is then positioned vertically upon asuitable support. Thereupon the granular non-cementitious insulatingmaterial is introduced by gravity into the sheath through the open upperend thereof as by means of a funnel 25. The support will preferably bevibrated vertically to a slight degree to insure complete filling of thesheath.

While various granular non-cementitious insulating materials, as, forinstance, quartz sand, have been found practical, I prefer to employmagnesium oxide because of the good heat conducting and dielectricproperties thereof when treated in the manner herein contemplated by me.When the sheath has been filled the remainder of the edge portions 24bof the cover plate 24 are bent into overlapping relation to flanges |00,as shown in Figs. 3 and 4, to completely close the sheath. Thereafterthe heater is placed in a pressure die and subjected to a relativelyhigh pressure between points indicated at 26 and 21. This portion of thesheath is thus reduced in thickness and the granular insulating fill iscrushed and highly compacted Ywhereby the resistor helix is positivelyfixed in spaced relation to the inner walls of the sheath, whereas thecompaction of insulation affords a good path for conduction of heat fromthe resistor. At any stage following the overlapping of end portions 24aof cover plate 24 the completely assembled heater is provided atopposite ends with suitable openings 28 and 29 to provide for attachmentof the heater to a support.

Figs. 5 and 6 depict an embodiment of the invention wherein bothterminals are located at the same end of the sheath. At the end of thesheath not having said terminals, the bottom wall of said sheath partI0a has attached thereto as by means of Welding a bracket I5 abovedescribed. To insure centrally locating the resistor 3| within thesheath it is necessary to provide said bottom wall of sheath part Illewith a protuberance 30 to which said bracket I5 is attached asdescribed. Each of the ends of bracket I5 has attached thereto a ring I6and a sheet metal supporting member i'I. As shown in Fig. 6, the helicalresistor 3| in this embodiment is of substantially the same diameter asthat of resistor 23 of the first described embodiment, and like said rstdescribed embodiment is reflexed between the brackets I5 (Fig. 6).

While I have described in detail herein the method of and means forproducing an electrical heater of the strip type it is to be understoodthat certain features of the invention have utility as applied toelectric heaters of other types. Also it will be apparent that variouschanges and modifications can be made without departing from the scopeof the invention.

I claim:

l. A resistor supporting and wiring terminal assembly for electricheaters of the sheath type, comprising a bolt having a fiat head to bepositioned within the sheath of the heater, a stamped sheet metal memberwelded to said head, said member having portions offset from said head,one of said portions constructed with clamping means to securely engagethe end of a wire resistor, means attached to said other offset portionand including a fiat mica insulating member for holding a reexed portionof the wire resistor in spaced relation within said sheath.

2. A resistor supporting and wiring terminal assembly for electricheaters of the sheath type. comprising a bolt having a flat head to bepositioned within the sheath of the heater, means attached to said boltfor anchoring said bolt against rotational displacement relative to saidsheath, a stamped sheet metal member welded to said at head, said memberhaving portions offset from said head, the end of one of said portionsbeing hook-shaped to clampingly engage the end of a wire resistor, theother of said offset portions having means attached thereto andinsulated therefrom to receive a relexed portion of the resistor tomaintain said reflexed portion in a predetermined position Within saidsheath.

3. A resistor supporting and wiring terminal assembly for electricheaters of the sheath type, comprising a bolt having a flat head to bepositioned within the sheath of the heater, means associated with saidbolt for anchoring said bolt against rotational displacement relative tosaid 5 sheath, a stamped sheet metal member welded to said bolt head,said member having hookshaped end portions oiset from said head, one ofsaid end portions clampingly engaging the end of a Wire resistor, theother of said oiiset portions having an insulating member attachedthereto, and means cooperating with said insulating member to position areiiexed portion of the resistor Within said sheath.

4. For a sheathed electric heater of the strip type having a reflexedresistor, a substantially flat resistor supporting assembly comprising astamped sheet metal member positioned Within the sheath and formed withan oiset portion, a flat mica insulating member attached to said oisetportion and a supporting member attached to said insulating member forsupporting a reflex of the resistor in insulated relation to said sheathand to said sheath metal member.

5. For a sheathed electric heater of the strip type having a reexedresistor, the number of reflexes depending upon the heater size andarrangement desired, a resistor supporting and Wiring terminal assembly,comprising a bolt having a flat head to be positioned within the sheathof the heater, a stamped sheet metal member welded to said head andformed with a plurality of offset portions, means including aninsulating member and a supporting member attached to said insulatingmember, one of said offset portions being adapted to clampingly retainan end of the Wire resistor and the other 6 of said oset portions beingadapted to retain said insulating member for supporting said reflexedresistor in insulated relation to said sheath and to said sheet metalmember.

6. For a sheath type electric heater having a reexed resistor, thenumber of reflexes depending upon the heater size and arrangementdesired, a resistor supporting and wiring terminal assembly, comprisinga bolt positioned partly Within the sheath of the heater, a sheet metalmember attached to said bolt Within said sheath and formed with anoiiset portion, said offset portion being formed with a hook toclampingly engage the end of the Wire resistor and said portion beingformed with a second hook to engage an insulated supporting member towhich is fastened one of the reflexes of said resistor to therebyposition said reflex within said sheath.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,143,578 Denhard June 15, 1915 1,904,594 Abbott Apr. 18, 19331,993,410 Lightfoot Mar. 5, 1935 2,091,839 Tangeman Aug. 31, 19372,286,090 Harrison June 9, 1942 FOREIGN PATENTS Number Country Date620,499 Great Britain Mar. 25, 1949

